Product Safety Assessment (PSA): WideStrike™ Insect Protection
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- WideStrike™ Insect Protection is a new, combined insect-protection trait developed for use in cotton. WideStrike Insect Protection was developed by Dow AgroSciences and utilizes the cry1F gene and cry1Ac gene in genetically modified cotton. Both genes express insecticidal proteins (called Cry1F and Cry1Ac) derived from different strains of a naturally occurring soil micro-organism, Bacillus thuringiensis (Bt). For more information on Bt, Cry1F, and Cry1Ac, see Product Description. WideStrike Insect Protection offers a high level of protection from several economically significant insect pests including tobacco budworm, cotton bollworm, fall armyworm, pink bollworm, loopers and several other species listed in the Product Description.
- WideStrike Insect Protection provides season-long, whole-plant protection from insect feeding damage, which allows cotton plants to remain healthier throughout the growing season. Full-season protection against insect damage facilitates cotton varieties reaching their full genetic growing potential and enhances yield potential for the cotton plant. WideStrike Insect Protection can also increase farmers' productivity by reducing various inputs (e.g., labor, fuel, equipment, pesticides) typically required for conventional insect control programs.
- On the basis of rigorous testing, regulatory agencies concluded that cotton with WideStrike™ Insect Protection is as safe as conventional, non-transgenic cotton. The primary route of potential exposure would occur through ingestion. The proteins in WideStrike Insect Protection are present in common soil organisms, so exposure can also occur naturally but at much lower levels (see Exposure Potential and Health Information). Extensive safety data was provided by Dow AgroSciences LLC to the U.S. Department of Agriculture (USDA), Environmental Protection Agency (EPA), and the Food and Drug Administration (FDA) before cotton with WideStrike Insect Protection was approved for sale (see Environmental Information and Health Information).
Plant biotechnology can be defined as a precise process in which scientific techniques (e.g., genetic modifications) are used to develop useful and beneficial plants with desirable “traits”. A trait refers to characteristics that are associated with the plant, including agronomic qualities and resistance to insects, herbicides, and disease. Plant biotechnology first identifies the genes responsible for the desired trait and then transforms them into plant cells. The trait may come from the plant itself (in this case cotton) or from a very specific gene of another organism, such as a bacterium.
DNA is the “genetic backbone” found in all microorganisms, plants, animals and humans. Organisms that carry DNA introduced via genetic modification are referred to as transgenic, and the introduced DNA is termed a transgene. The first step in creating WideStrike™ cotton was the isolation and replication of DNA segments from different strains of Bacillus thuringiensis that were responsible for the expression of the desired insecticidal proteins (Cry1F and Cry1Ac). The isolated DNA fragments were then chemically re-synthesized to create the final transgenes, including plant-preferred DNA sequences that optimize expression of the insecticidal proteins in the plant.
As shown in Figure 1, a transgene is comprised of a protein coding region, a preceding promoter element and a trailing regulatory element. The promoter element determines the strength at which a trait will be expressed in the plant. The promoter also determines in which plant tissues the trait will be expressed. The trailing regulatory element defines the length of the DNA to be expressed. WideStrike cotton is a stack of two independent transgenic events engineered with cry1F and cry1Ac genes. The Cry1F event is comprised of a cry1F protein coding region, the 4ocs ∆mas promoter and orf25 trailing regulator element. The Cry1Ac event is comprised of a cry1Ac protein coding region, the maize ubiquitin-1 promoter and orf25 trailing regulator element. It is critical that both Cry1F and Cry1Ac expressions are maintained at their optimal level in order for the trait to exhibit its characteristics.
A “selectable marker gene” is normally associated with a gene of interest during plant transformation. Selectable marker genes can be used in both the laboratory and the field to quickly determine if plants contain the desired genes and are expressing the desired proteins. For WideStrike Insect Protection, the pat gene is used as the selectable marker. (For more information on PAT, see Product Description). The pat gene, which is located next to the cry1F gene and cry1Ac genes, is controlled by a different promoter, and the same bi-directional trailing regulatory element. The pat gene provides a certain level of tolerance to glufosinate-ammonium and facilitates the selection of plants containing Cry1F and Cry1Ac.
Once the transgenes were constructed, they were then inserted into plant tissue through process known as transformation. WideStrike Insect Protection was created through Agrobacterium-mediated transformation of cotton. Agrobacterium is a naturally occurring soil pathogen that can transfer and integrate selected DNA in a stable fashion into the cotton plant. Sections of immature cotton tissue (cotyledons) were incubated on artificial media with special strains of Agrobacterium that transferred the desired DNA into the cotton plant cells. Transformed cells were then isolated by growing plants on a selective medium and transgenic plants subsequently regenerated. Once integrated into the plant's genome, the transgene was inherited through normal sexual reproduction.
Each transformation experiment produced an “event” and many events were created to identify the optimal balance between protein expression and agronomic quality of the cotton plant. For WideStrike™ cotton, the final events chosen during the “event sorting” process were known by the designation 281-24-236 (Cry1F) and 3006-21-23 (Cry1Ac). The two cotton events were then combined through traditional plant breeding techniques to form cottonseed expressing the Cry1F and Cry1Ac proteins.
Numerous tests and checks are in place to ensure quality of the genetically modified seed and, ultimately, the generations of seed formed afterward. WideStrike cotton was exhaustively tested for the stability of the trait through several growing cycles, for safety to animals, humans and the environment, and for retention of nutritional value.
Now that this process has proven successful on all counts, and WideStrike™ Insect Protection has been approved by the USDA, FDA and EPA as well as other regulatory agencies globally, the genetically modified material is sold to farmers to grow for production of fiber, cottonseed meal and hulls for livestock consumption, and cottonseed oil for human consumption. Successful development of genetically modified crops requires a deep understanding of the food chain, biology, regulatory requirements and more.
The product that is purchased is seed cotton with WideStrike Insect Protection. The protection is achieved by genetically modifying the cotton to include two genes which express proteins making it resistant to certain insect pests. The expression of the new proteins (Cry1F and Cry1Ac) by the new genes (cry1F and cry1Ac) allows the plants to produce the same proteins as are produced by the naturally occurring soil bacteria from which the genes were isolated. Following is background information about each protein and their effects.
Cry1F, Cry1Ac and Bt – The cry1F gene, isolated from the common soil bacterium Bacillus thuringiensis var. aizawai (often referred to as Bt), produces the Cry1F protein. The cry1Ac gene (which produces the Cry1Ac protein) was isolated from a different strain of Bt (subsp. kurstaki). Bt was first discovered in 1901 by the Japanese biologist S. Ishiwatari as the source of disease that was killing large populations of silkworms. Bt was first used as an insecticide in 1920, and spray formulations containing either Bt bacteria or Bt proteins have been used for more than 40 years for crop protection, including organic farming operations. EPA-approved Bt insecticides saw expanded use and development in the 1980s as an alternative to synthetic chemical insecticides.
Beginning in the 1980’s, the genes responsible for making Bt proteins were isolated and transferred into crop plants. In the United States, Bt was first commercially approved in transgenic cotton seed in 1995. Compared to conventional Bt spray formulations, transgenic plants with the Bt protein provide much more effective insect protection throughout the growing season. Other Bt proteins besides Cry1F and Cry1Ac have been used to genetically modify commercial crops including potatoes, corn, and cotton.
Bt must be ingested to kill the insect. A susceptible immature insect (larva) eats the protein, which then binds to specific receptors in the larva's gut. Binding initiates a cascade of effects in the larva that ultimately leads to death.
Bt proteins are highly selective on only certain categories and/or species of insects. The Cry1F and Cry1Ac proteins affect the larvae of damaging lepidopteran (moth) species on cotton that include tobacco budworm, cotton bollworm, fall armyworm, southern armyworm, beet armyworm, pink bollworm, cabbage looper, soybean looper, saltmarsh caterpillar, European corn borer, cotton leaf perforator, omnivorous leafroller, and citrus peelminer. The most damaging pests in the United States cotton belt are the tobacco budworm and cotton bollworm. In the United States, the combined cost of controlling these two pests and the losses they inflict on cotton production exceeds $300 million a year.
Cry1F and Cry1Ac proteins are expressed at effective concentrations throughout the growing season of WideStrike cotton. Targeted insect larvae are exposed to the insecticidal protein at all stages in their life cycle. Thus, WideStrike cotton provides season-long protection against targeted pests.
Cry1F and Cry1Ac have been found to not adversely affect beneficial insects or other organisms, including honeybees, earthworms, lady beetles, springtails and green lacewings. For more information, see Environmental Information.
PAT – Phosphinothricin-N-acetyltransferase (PAT) is an enzyme isolated from the common soil bacteria Streptomyces viridochromogenes. Used as the “marker gene”, PAT imparts transgenic plants with tolerance to the herbicide glufosinate-ammonium and facilitates the selection of plants containing Cry1F and Cry1Ac. Glufosinate-ammonium was developed from the same bacteria as PAT and causes ammonia to build up in the plant tissues. Excess ammonia disrupts cell membranes and stops photosynthesis. This eventually kills the plant (either non-transformed cotton or certain species of weeds). PAT is essentially the antidote to glufosinate-ammonium, allowing the plant to detoxify the chemical.
Cotton seed with WideStrike Insect Protection is used to produce high quality cotton with greater efficiency for higher yields, and less loss due to insects. It can also greatly reduce the number of pesticide applications usually required for common lepidopteran insect pests. WideStrike cotton may be used for production of fiber, cottonseed meal and hulls for livestock consumption, and cottonseed oil for human consumption.
The Cry1F, Cry1Ac and PAT proteins are present in common, non-pathogenic soil bacteria, so exposure can occur naturally and without concern. WideStrike cotton may be used for production of fiber, cottonseed meal and hulls for livestock consumption, and cottonseed oil for human consumption. Thus, consumers may wear or eat processed cotton products which utilized the WideStrike trait. However, none of the three expressed proteins are detectable in the oil, meal, and hulls of WideStrike cotton. Processed linters are composed of pure (>99%) cellulose and are treated with heat and solvent that remove and destroy any residual protein. Several studies have demonstrated the human and animal safety of proteins used in WideStrike cotton. Neither protein is associated with toxicity or allergenicity. See Health Information.
Farmers and cotton-gin workers may be exposed to harvested cotton. Since WideStrike™ Insect Protection is as safe as cotton without it, standard workplace procedures and precautions should be followed. See Health Information.
On the basis of rigorous testing, WideStrike Insect Protection has received full food, feed and environmental approval by regulatory agencies in the United States. The EPA found that WideStrike Insect Protection does not pose risks to human health and is as safe as products from conventional cotton. Cry1F, Cry1Ac and PAT are present in soil bacteria and are not considered pathogens of humans or animals. None of the expressed proteins in WideStrike Insect Protection has biochemical characteristics or homology (relevant similarities) with known food allergens or toxins, indicating that WideStrike Insect Protection is highly unlikely to pose any risk of allergic reaction.
Acute mouse oral toxicity studies conclude that the three proteins expressed in WideStrike™ cotton do not pose any toxicological risk to human and animals. There are no differences in the nutrient composition of respective oil, meal or hull products between WideStrike and conventional cotton. WideStrike cottonseed oil and meal are as nutritious as those made from conventional cotton varieties. Poultry feeding studies prove no difference in body weight gains between chickens fed with WideStrike cottonseed meal and conventional cottonseed meal.
Seed Treatments – Agricultural seeds, including cotton with the WideStrike trait, may be treated with an insecticide and/or a fungicide and these seed treatments can present certain health risks. These risks are associated with the seed treatments and not the WideStrike™ trait. Consult the appropriate Safety Data Sheet (SDS) and/or label or tag for seed treatment hazard information, and wear all recommended personal protective equipment.
Herbicide-tolerant Traits – Many cottonseed products with the WideStrike trait will also have a trait that provides tolerance to the herbicides such as glyphosate (e.g., Roundup Ready®). Consult the appropriate SDS for the safety profile and precautions associated with this trait.
Before a biotech product can be introduced to the market, approval by appropriate governmental agencies is required. Using the criteria established by these agencies, Dow AgroSciences conducts extensive, validated tests for its biotech products. For the approval of cotton in the United States with the WideStrike trait, extensive safety and environmental data was provided to the USDA, EPA, and FDA as part of a pre-market consultation process.
Cotton with the WideStrike trait produces minute quantities of the Cry1F and Cry1Ac proteins, contained in the plant and plant parts such as leaves, squares, flowers and cottonseed. Both proteins degrade rapidly in the soil, minimizing the potential for run-off or exposure to soil-dwelling non-target organisms.
A number of non-target organisms were tested as part of the registration process for WideStrike™ Insect Protection and no adverse effects were observed. Some of the organisms tested include honeybees, earthworms, lady beetles, springtails and green lacewings. No adverse effects were observed in birds or fish. In addition, there is very low risk for impact on Monarch butterflies, and this product has no adverse effects on endangered species.
Another important environmental consideration with a biotech product is how cross-pollination will affect the environment. Cotton (Gossypium hirsutum) is mainly a self-pollinating plant and the chance for gene exchange between cotton with the WideStrike trait and other cotton varieties is possible yet minimal due to mandated isolation growing distances and various environmental/biological factors. In the U.S. the risk of gene flow to other related cotton species (either under cultivation or wild) is very unlikely. There is no selective advantage for cotton varieties with WideStrike Insect Protection in the natural environment.
There is a potential long-term risk of target pest adaptation to the Cry1F and Cry1Ac proteins leading to the possibility of reduced efficacy. An insect resistance management plan is in place with growers to mitigate this risk.
Regulations may exist that govern the manufacture, sale, transportation, use, and/or disposal of cotton with the WideStrike trait, especially if the seed is treated with an insecticide or fungicide. These regulations may vary by city, state, country or geographic region. Please review the SDS and product label for the product you are using.
- Dow AgroSciences WideStrike Product Web Site
- Expanded technical summary and additional references that support the information summarized here on WideStrike™ traits can be found at Agbios web site
- USDA notice of deregulation [http://www.aphis.usda.gov/brs/aphisdocs2/03_03601p_com.pdf] and [http://www.aphis.usda.gov/brs/aphisdocs2/03_03602p_com.pdf]·
- EPA Biopesticide Registration Action Document
- FDA Consultation Note to File
For more business information about WideStrike Insect Protection, visit the Dow AgroSciences web site.
Last Updated: May 2, 2006
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™WideStrike is a trademark of Dow AgroSciences LLC
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